Date of Degree
Lisa L. Manne
Caterpillar Biomass; Demography; Ecological Modeling; Habitat Quality; Phenology; Setophaga
Monitoring bird populations becomes more complex as climate change alters species' relationships with their habitats. The presence of a species does not necessarily indicate a thriving population; in fact, we expect to see changes in demography and nest success before extinction at a site. Here, I first model aspects of demography as a proxy for habitat quality across a large portion of a species' range, using land cover and climate predictors. I show a gradient of high to low habitat quality from north to south within the range for the Yellow Warbler (Setophaga petechia), with summer temperature and amount of habitat cover being important predictors. However, these relationships with habitat are not fixed across time, especially as climate alters the phenology of trees and important insects that these birds rely on to feed their nestlings. Little is known about the phenology of caterpillar biomass availability in North America, and since many birds have specific breeding habitat and foraging niches, the phenology and caterpillar biomass availability from specific tree species may be important to the persistence of certain bird species. In Chapter III, I model caterpillar biomass curves through time for eight tree species using random intercept mixed-effects models and find differences in the availability of caterpillar biomass among tree species. In addition, I test for differences in caterpillar biomass availability during the breeding period for four species of long-distance migratory warblers with different nesting and foraging niches, finding that tree species such as Red Oak (Quercus rubra) provide the majority of caterpillar biomass to these birds. However, species assemblages, species phenology, and species' phenological responses to climate change vary across large spatial scales, so extrapolating caterpillar biomass availability across these large scales is problematic. Chapter IV tests how well a remotely-sensed measure of greenness commonly used as a measure of tree phenology, the Normalized Difference Vegetation Index (NDVI), correlates with caterpillar biomass in each of these tree species. Interestingly, the caterpillar biomass from most tree species correlates synchronously with NDVI in 2014, but lags NDVI in a year with anomalously warm spring temperatures. This suggests that although NDVI may be a good proxy for caterpillar biomass in some years, caterpillars and their trees are likely to be susceptible to phenological mismatches as climate anomalies become more common. My dissertation chapters highlight the importance of monitoring phenology range-wide in as many taxa as possible in order predict how interspecific relationships will change with changing climate.
Ozelski, Ashley, "Climate, Resource Phenology, and Demographic Population Structure Impacts on Songbird Habitat Quality" (2015). CUNY Academic Works.